The invention is especially applicable to the repositioning of spacers in fluid-cooled nuclear reactors. In a fluid-cooled nuclear reactor, such as a Candu reactor, having a calandria comprising an array of calandria tubes each housing a coolant tube extending coaxially therethrough, the coolant tubes are generally spaced from the respective calandria tubes in which they are housed by annular spacers, such as "garter springs". The spacers are necessary to maintain the coaxial relationship of the tubes, and above all to prevent them from coming into contact as local overheating would cause structural damage.
In the installation of such a reactor, or even during its operation, spacers may be displaced from their required positions with the result that the coolant tubes will lack the necessary configuration of supports to carry the distributed load in operation of the reactor, and serious problems may arise from sagging of these tubes. For safe operation of such a reactor it is therefore necessary to have some way of repositioning the spacers after installation or even after the reactor has been operating for some time. However, these spacers are seated between the coolant tubes and the calandria tubes and are not directly accessible by mechanical means and so repositioning of the spacers has hitherto necessitated extensive dismantling of the calandria.
The present invention provides an alternative method for repositioning the spacers which does not require direct mechanical access to them and which in consequence is simpler and much less costly than hitherto known methods.